1. Technical Field
The present invention relates to a motor controller, and more specifically to a motor controller, which can control the power factor, limit a high frequency current, and eliminate noise components, that is, ripple components of an input current.
2. Background Art
A motor controller is an apparatus for converting AC power into DC power and converting the DC power into AC power again in order to drive a three-phase motor. The motor controller has been used in various fields over the length and breadth of the industry. For example, the motor controller has been used in air conditioners, including washing machines and refrigerators, elevators, vehicles, and so on.
FIG. 1 is a circuit diagram showing a conventional motor controller.
Referring to the drawing, a conventional motor controller 100 boosts three-phase AC power using reactors La and Lb, converts AC power into DC power using a converter 110 having switching elements, and smoothes voltage rectified by a smoothing capacitor C.
An inverter 120 includes switching elements. The inverter is supplied with smoothed DC power, and converts the DC power into three-phase AC power having a specific frequency through switching operations and applies the AC power to a three-phase motor 150.
A microcomputer (not shown) outputs a switching control signal Sc for driving the switching elements of the converter (not shown) based on voltage of the converter output terminal. Further, the microcomputer (not shown) outputs a switching control signal Si for driving the switching elements of the inverter 120 based on an output current of an inverter output terminal.
Typically, when referring to the motor controller as shown in FIG. 1, in the case in which voltage received through the reactors La and Lb from a three-phase AC power source is converted into a DC voltage, power factor control and DC voltage boosting are performed by the switching operations of the converter 110. However, since the switching elements of the converter 110 are switched at high speed, a harmonic current of a high frequency is generated. This high frequency current flows back to a system coupled to the three-phase AC power source and therefore affects other devices coupled to the system.
In the case in which the motor 150 is driven using the three-phase AC power source as described above, the operations of circuit elements within each device may become unstable by the harmonic current of a high frequency, which flows through the system or from the system to a motor driving apparatus. Accordingly, there is a possibility that reliability may be degraded.
With respect to this high frequency harmonic current, each country has prepared an additional regulation scheme. In particular, EN 6100-3-2 by the European Union (EU) has provided regulations for high-frequency harmonic current restriction regarding the current of 16 A or less and EN 6100-3-12 regarding the current of 16 A or more.
Meanwhile, the harmonic current is limited by the reactors La and Lb of FIG. 1 to some extent, but not only the harmonic current, but also noise components of an input current, etc. are not eliminated.